By means of cell transfers between allotype(Igh)-congenic mouse strains, we have shown Igha mice to contain T cells that can prevent both the production of a specific B cell allotype (Igh-1b) in normal and in athymic Ighb mice - and the growth of an established line of Igh-1b-producing tumor cells. We have referred to these cytotoxic (c) or suppressor (s) T cells as Igh-1b Tcs cells. Recently, we succeeded in adapting long-term, cultured lines of Igha T cells that specifically kill Igh-1b tumor cells in vitro; several of these Igh-1b Tc cell lines also have been shown capable of suppressing Igh-1b production in vivo. We propose to use clones of Igh-1b Tc cells as a model system for investigating how T cells can recognize and control the proliferation of a specific population of B cells. We have evidence this involves a T cell receptor specific for Igh-1b; therefore, we are particularly interested in characterizing this receptor and the gene(s) responsible. To do this we will take as a given that antigen-specific receptors on both T and B cells are encoded (in part) by Heavy chain variable region (VH) genes. Thus, select B cell hybridomas that produce receptors (antibodies) specific for Igh-1b will be used for the construction of relevant cDNA probes. Probes will be made specific for VH genes and used to examine clones of Igh-1b Tc cells that express VH idiotypes identical or similar to those of the B cell hybridomas. Igh-1b Tc cell lines lacking the appropriate VH idiotype along with unrelated cell lines of T and B tumors will serve as negative controls.